This research involves developing procedures to determine regional flow in tissues and organs at high resolution. Current methods for regional flow determinations are limited by microsphere size and counting statistics. This study tests the hypothesis that fluorescently-labeled antibodies, serving as "molecular microspheres", will attach to capillary binding sites in proportion to microregional flow. As compared to current microsphere-based measurements, the fluorescence intensity from bound dye molecules could potentially improve volume resolution of regional flow measurements by factors of 1,000 to 1,000,000. The project will develop fluorescence image analysis methods to measure microregional flow in whole organs. This project will provide physiological/medical researchers with a unique tool for quantifying regional flow at high resolution.. Phase I research will demonstrate the ability of fluorescent antibodies to serve as molecular flow markers in rat heart. Phase II will extend this methodology to studies of different colored fluorochromes attached to antibodies and to different antibodies specific to capillary endothelium. Phase II will also demonstrate the utility of the method for flow measurements in different organs and large animals and will develop high resolution flow display software. This technological innovation will advance the development of the Imaging CryoMicrotome/TM to perform integrative physiological studies in tissues and organs. PROPOSED COMMERCIAL APPLICATIONS: Potential markets include the hundreds of laboratories that currently do low resolution flow measurements, as well as researchers wishing to validate MRI methods on experimental animals. Increasing the resolution (decreasing tissue volume element size) could greatly expand the types of studies using this technology and increase demand for cytomicrotome imaging.